1. Field of the Invention
The present invention relates to an isostatic press for high pressure treatment of a product in the pressure chamber of the isostatic press. The invention also relates to a method, a container, and a plant for high pressure treatment of a product by means of such an isostatic press.
2. Description of the Related Art
Isostatic presses of the type mentioned by way of introduction have different ranges of application. One range of application is isostatic high pressure treatment of products such as foods, drugs and cosmetics. Isostatic high pressure treatment of this type aims at inactivating undesirable microorganisms and enzymes in the product, thereby extending the shelf life of the product without detrimentally affecting the quality of the product. Compared with traditional methods for heat treatment, isostatic high pressure treatment is particularly suitable for foods since the natural flavors, scents and nutritive substances of foods are better preserved and the process times are shorter. Isostatic high pressure treatment implies that the product is subjected to the same pressure from all sides, which means that the product, even if it shrinks, will not change its geometric shape during treatment. The pressure in the isostatic press in high pressure treatment of foods typically amounts to about 2000-10000 bar. However, in some isostatic presses a higher pressure can be applied, such as up to about 15000 bar.
In isostatic high pressure treatment of foods and similar products, it is desirable to separate the food product from the pressure medium in the isostatic press. In prior-art technique, this is done by placing the food product in a package made of a flexible material that allows pressure transfer from the pressure medium to the product that is to be treated. Typically, said package is made as a flexible trough or a bag which is in direct contact with the pressure medium in the isostatic press. By increasing the pressure in the isostatic press, the increased pressure is transferred to the product through its flexible package, and the product will thus be treated.
In isostatic high pressure treatment of foods and similar products, the isostatic press and the pressure medium in the isostatic press typically have a temperature of about 10-120° C. The product that is to be subjected to high pressure treatment will during treatment assume substantially the same temperature as the isostatic press, which in many cases is also preferred. In prior-art technique, it is presently aimed at providing isostatic presses where the temperature of the product and the isostatic press should be significantly the same during the entire treatment. One problem remains, however, when products are to be subjected to high pressure treatment in a frozen state without thawing during the treatment, since it has been found difficult to use an isostatic press which in operation has the same low temperature as the frozen product.
Today there is a need to be able to subject frozen products to high pressure treatment, without thawing. Traditional isostatic presses do not present any possibilities of high pressure treatment of frozen products without thawing, and therefore improvements are required for the purpose of eliminating this problem.